Vehicle occupant restraint system and method for operating a vehicle occupant restraint system

ABSTRACT

The invention describes a vehicle occupant restraint system ( 2 ) comprising a control unit and at least two restraint elements ( 8, 10 ) for the protection of lower extremities ( 6, 6′, 7, 7′ ) in the area of a footwell ( 4 ) of a vehicle of a vehicle occupant seated in a particular vehicle seat of the vehicle, wherein a first restraint element ( 8 ) is configured as a knee airbag module ( 12 ), wherein a second restraint element ( 10 ) is provided for mounting into the footwell ( 4 ) of the vehicle, especially in an area of the footwell ( 4 ) of the vehicle arranged in the vehicle longitudinal direction (x) ahead of the knee airbag module ( 12 ), wherein, in a situation of restraint, the control unit can differentiate between different given situations, wherein the given situation can be determined via a vehicle seat position and parameters relating to vehicle occupants, wherein, in the situation of restraint, when a situation is given in which the vehicle seat ( 5 ) is in a position shifted backwards, especially in a position shifted backwards compared to the standard position, and the vehicle occupant is a short and/or light person, the control unit only activates the foot airbag module ( 16 ) of the second restraint element ( 10 ).

RELATED APPLICATIONS

The present invention is a U.S. National Stage under 35 USC 371 patentapplication, claiming priority to Serial No. PCT/EP2019/070810, filed on1 Aug. 2019; which claims priority from 10 2018 118 903.6, filed 3 Aug.2018, the entirety of both of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to a vehicle occupant restraint system comprisinga control unit and at least two restraint elements for the protection oflower extremities in the area of a footwell of a vehicle of a vehicleoccupant seated in a particular vehicle seat of the vehicle and to amethod for operating the vehicle occupant restraint system according tothe invention.

PRIOR ART

For protecting the lower extremities of a vehicle occupant in asituation of crash, in vehicles increasingly vehicle occupant restraintsystems comprising especially knee airbag modules including knee airbagshave been used in the area of the footwell. In a situation of crash,those knee airbags can both prevent the knee and/or the shin (tibia) ofthe vehicle occupant from directly impacting on an instrument panel andminimize the risk of vehicle occupants slipping under a seatbelt in thesituation of restraint.

The progressive developments in the field of automated and autonomousdriving may result in seat adjusting options for the vehicle occupantswhich are located beyond a standard position or a standard positionrange of the vehicle seat for which the existing vehicle occupantrestraint systems are designed. In those comfort positions, the vehicleseat is especially in a position adjusted further backwards or in aposition having a strongly reclined seat back.

This results in the fact that the positions of the vehicle occupantsrelative to the restraint systems usually tightly mounted on the vehiclestructure such as especially airbags, may be variable during travelingand, as compared to the standard position range, the distances may besignificantly increased depending on the situation. Further, therelative position of the vehicle occupants may thus deviate from thestandard position such that restraint systems installed on the vehiclestructure cannot or do not fully become effective.

SUMMARY OF THE INVENTION

Therefore, it is the object of the invention to provide an improvedvehicle occupant restraint system for protecting the lower extremitiesof a vehicle occupant. In particular, it is the object of the inventionto provide a vehicle occupant restraint system for protecting the lowerextremities of a vehicle occupant by which the protective effect of thevehicle occupant restraint system can be improved irrespective of therelative position of the vehicle occupant.

Achieving the Object

The features according to the claims lead to achieving the object.Advantageous configurations are described in the subclaims.

Expressions of place such as “in front of” and “behind” as well as“upper” or “lower” relate to a vehicle longitudinal axis and, resp.,vehicle vertical axis of a vehicle.

A vehicle occupant restraint system according to the invention isprovided for protecting lower extremities of a vehicle occupant who isseated in a particular vehicle seat. The vehicle occupant restraintsystem according to the invention comprises at least two restraintelements and a control unit. The at least two restraint elements of thevehicle occupant restraint system are disposed, for the protection ofthe lower extremities of the vehicle occupant, in a state installed inthe vehicle in the footwell or at least in the area of the footwell ofthe vehicle.

A first restraint element of the vehicle occupant restraint systemaccording to the invention is in the form of a knee airbag module. Theknee airbag module is disposed, in a typical embodiment in the stateinstalled in the vehicle, in a lower area of the instrument panel. Theknee airbag module may be configured especially as a so-called“low-mounted module” or “mid-mounted module”.

A second restraint element of the vehicle occupant restraint systemaccording to the invention is provided for being installed in thefootwell. The second restraint element is disposed or, resp., mounted inthe state installed in the vehicle especially in an area of the footwelllocated in front of the knee airbag module.

The second restraint element comprises at least one foot airbag moduleincluding a foot airbag. The foot airbag module can be especiallyconfigured as a partial element of the second restraint element.

The control unit of the vehicle occupant restraint system according tothe invention can differentiate, in a situation of restraint, betweendifferent given situations.

The classification of the different situations by the control unit isbased especially on parameters relating to vehicle occupants and/or on aposition of the vehicle seat relative to the first and second restraintelements disposed in the area of the footwell.

Concerning the vehicle seat position, a distinction can especially bemade between a standard position and a comfort position of the vehicleseat. The standard position describes a standard position of the vehicleseat for which restraint elements of a vehicle occupant restraint systemfixedly arranged in the vehicle structure are designed. The comfortposition describes especially a position of the vehicle seat in whichthe vehicle seat is shifted backwards and has a larger space from therestraint elements of the vehicle occupant restraint system than in thestandard position.

The parameters relating to vehicle occupants may be especially the bodyweight and/or a body height and/or a position of the vehicle occupant inthe vehicle seat. Further, the parameters relating to vehicle occupantsmay as well relate to a position of the lower extremities in thefootwell of the vehicle.

In the vehicle occupant restraint system according to the invention, ina situation of restraint only the foot airbag module of the secondrestraint element is activated by the control unit, if the control unitdetects a situation in which the vehicle occupant is a short and/orlight person and the vehicle seat is in a position shifted backwards,especially in a position shifted backwards vis-à-vis the standardposition.

In a situation in which the vehicle seat is in the standard positionand/or the vehicle occupant is not a short and/or light person, in thesituation of restraint, on the other hand, at least the knee airbagmodule (12) of the first restraint element (8) is activated by thecontrol unit. Moreover, depending on the given situation, the secondrestraint element or a partial element of the second restraint elementcan additionally be activated by the control unit.

For this purpose, the vehicle occupant restraint system may include acontrol unit for controlling and activating the first and/or secondrestraint element(s). Preferably, the control unit of the vehicleoccupant restraint system may be integrated in a vehicle control system,especially in an airbag control system. In particular, the control unitmay be integrated in a vehicle control system by which further restraintsystems can be additionally activated and controlled.

For determining the parameters relating to vehicle occupants and/or therelative position of the vehicle seat, the vehicle occupant restraintsystem can comprise at least one sensor element. Alternatively, oradditionally, the control unit can access the sensor data of one or moresensor elements integrated in the vehicle. The sensor element maycomprise a camera system, for example. Furthermore, the sensor elementcan include, e.g., one or more sensors integrated in vehicle seatelements. In addition, the control unit can preferably make also use ofand/or access sensor data of further sensor elements arranged in thevehicle, especially in the footwell, for detecting the given situation.

The foot airbag module is preferably arranged in the lower area of theinstrument panel in the vehicle longitudinal direction ahead of the kneeairbag module. Preferably, in a filled state, the foot airbag isarranged beneath and/or ahead of the foremost and lowest knee airbagchamber. The low-pressure chamber offers substantially the sameadvantages and properties as the low-pressure chamber of the kneeairbag.

In typical embodiments of the vehicle occupant restraint system, thesecond restraint element moreover comprises a heel abutting pointpositioning module.

The heel abutting point can be adapted by the heel abutting pointpositioning module in the footwell of the vehicle in a restraintsituation. In particular, the heel abutting point can be shifted by theheel abutting point positioning module backwards in the vehiclelongitudinal direction and thus toward the vehicle occupant. Bydisplacing the heel abutting point toward the vehicle occupant, in asituation of restraint a forward movement of the lower extremities inthe area of the foot can be limited at an early stage, for example. Bylimiting the movement of the foot, e.g., the contact of the lowerextremities, especially of the knee and the shin, with the knee airbagcan be improved. Furthermore, this helps reduce, for example, the riskof the shin and the foot swinging upwards and rebounding from the kneeairbag. Moreover, for example, the risk of the shin and the footswinging upwards and passing under the knee airbag can be reduced. Theheel abutting point is shifted and positioned preferably by lifting thevehicle floor and/or the vehicle floor lining in the area of the heelabutting point positioning module. The heel abutting point mayespecially be an elevation or an edge in the area of the vehicle floorby which a forward movement of the foot can be inhibited and/or stoppedespecially in a situation of restraint.

Preferably, the heel abutting point positioning module is arranged, inthe mounted state in the footwell of the vehicle, in a transition areabetween the vehicle floor and a front wall delimiting the footwell. Thefront wall delimiting the footwell may be, for example, the bulkhead ofthe vehicle. Upon activation of the heel abutting point positioningmodule, the heel abutting point can be formed especially by a change ofcontour of the vehicle floor and/or of the lining of the vehicle floor.

The heel abutting point positioning module can comprise an airbag modulefor displacing and positioning the heel abutting point. Upon activationof the airbag module, especially the lining of the vehicle floor can belifted by filling the airbag of the airbag module and, thus, the heelabutting point can be shifted. The airbag of such heel abutting pointpositioning module usually has a slower fill rate, for example vis-à-visa knee airbag. The slower filling of the airbag of the heel abuttingpoint positioning module helps avoid high loads of the foot, forexample.

As an alternative, the heel abutting point positioning module maycomprise a deformation element. The deformation element is preferablydisposed between the vehicle floor and/or the front wall delimiting thefootwell and the lining of the vehicle floor.

In one embodiment, the deformation element is configured as a bistablespring element. Upon activation by the control unit, the bistable springelement can be excited, for instance through an actuator, to change itsshape from a first stable position to a second position.

In another embodiment, the deformation element comprises a foamableelement. The foamable element is made from a material that will foam byexcitation and will increase its volume. Upon activation of the heelabutting point positioning module by the control unit, said foamingprocess of the foamable element is started by an appropriate actuator.In this way, e.g., the lining of the vehicle floor is lifted and theheel abutting point is shifted toward the vehicle occupant.

It may further be provided that the heel abutting point positioningmodule is configured so that the positioning and thus the shift of theheel abutting point backwards toward the vehicle occupant takes placesuch that it is completed before the foot impacts on the heel abuttingpoint positioning module. This, too, helps avoid high loads of the foot.

In particular, the second restraint element may comprise especially botha heel abutting point positioning module and a foot airbag module. Eachof the heel abutting point positioning module and the foot airbag modulein such embodiment constitutes a partial element of the second restraintelement. In particular, the foot airbag module and the heel abuttingpoint positioning module can be activated independently of each other bythe control unit in the situation of restraint, in response to the givensituation.

The knee airbag of the knee airbag module of the first restraint elementpreferably comprises at least one adaptive chamber. The knee airbag maycomprise a pressure-adaptive chamber or a depth-adaptive chamber.Alternatively, the knee airbag may comprise a pressure-adaptive chamberand a depth-adaptive chamber. In one embodiment, such adaptive chamberof the knee airbag can be activatable and/or controllable through thecontrol unit.

In a typical embodiment, in a filled state of the knee airbag, thechamber of the knee airbag that is foremost and/or lowest in the vehiclelongitudinal direction and, resp., in the vehicle vertical direction isconfigured as a pressure-adaptive chamber of the knee airbag.

The pressure-adaptive chamber is preferably configured as a low-pressurechamber. The term low-pressure chamber can either describe that thepressure-adaptive chamber in a filled state has a lower internalpressure than the further chamber or, resp., the further chambers of theknee airbag. Alternatively, the term low-pressure chamber can describethat the pressure-adaptive chamber requires a significantly longerperiod of time until it is completely filled. In such embodiment, in asituation of restraint the low-pressure chamber is not completely filledwhen the shin (tibia) and/or the foot are/is impacting, and, thus, atthe time of impacting it has a lower internal pressure than the furtherchamber or further chambers of the knee airbag which is/aresubstantially completely filled at said point in time. The lowerinternal pressure of the low-pressure chamber helps reduce the risk, forexample, of the shin and the foot being rebounded after impacting on thelow-pressure chamber of the knee airbag.

The pressure-adaptive chamber can be configured, in one embodiment, suchthat the pressure-adaptive chamber can be filled in a situation ofrestraint, independently of the given situation. In particular, thepressure-adaptive chamber in such embodiment can be configured as alow-pressure chamber that is filled more slowly than the further chamberor the further chambers of the knee airbag by restriction of the flow ofthe fill gas, for example. It is also imaginable that an inflow orificeor an overflow orifice toward the pressure-adaptive chamber is closed byappropriate means in the event of a specific expansion or a specificinternal pressure of the pressure-adaptive chamber.

Alternatively, in one embodiment, the pressure-adaptive chamber can beactivated and, resp., controlled by the control unit. In particular, insuch embodiment, the pressure-adaptive chamber can be filled in responseto the given situation. For example, filling of the pressure-adaptivechamber can be carried out by an opening toward the pressure-adaptivechamber being released via a valve or a valve-like member.

In one embodiment, the knee airbag of the knee airbag module may beconfigured without a pressure-adaptive chamber. Preferably, the secondrestraint element in such embodiment comprises the foot airbag module.

The foot airbag of the foot airbag module may comprise a low-pressurechamber or may be configured as a low-pressure chamber. The low-pressurechamber offers substantially the same advantages and properties as thelow-pressure chamber of the knee airbag.

Especially a chamber of the knee airbag that is closest to the vehicleoccupant can be configured as a depth-adaptive chamber of the kneeairbag, based on a filled state of the knee airbag. A depth-adaptivechamber can help increase especially an expansion of the knee airbag inthe vehicle longitudinal direction. For example, in a comfort positionof the vehicle seat, a space between the knee of the vehicle occupantand the filled knee airbag can thus be reduced. The higher expansion inthe vehicle longitudinal direction and the space from the lowerextremities of the vehicle occupant reduced in this way can help limitthe forward movement of the vehicle occupant, for example, at an earlierstage in a situation of restraint.

Moreover, a depth-adaptive chamber can be arranged in the lower area ofthe knee airbag that faces the vehicle occupant's shin in the filledstate. By such configuration, especially the expansion of the kneeairbag in the direction of the vehicle occupant's shin is increased.Thus, for example, the shin and the foot can be prevented or at leastrestricted from swinging upwards.

Another substantial aspect of the invention is a method for operatingthe vehicle occupant restraint system according to the invention. Themethod comprises at least the following steps of:

-   -   detecting and determining a position of the vehicle seat and/or        parameters relating to vehicle occupants;    -   determining the given situation by the control unit;    -   activating the restraint elements required for restraint in the        given situation.

Depending on the embodiment, in the method according to the inventionthe position of the vehicle seat can be determined through at least onesensor element. Alternatively, parameters relating to vehicle occupantscan be determined through at least one sensor element. In anotherpreferred embodiment, the position of the vehicle seat and parametersrelating to vehicle occupants are determined through sensor elements.

When detecting the parameters relating to vehicle occupants, especiallya body weight and/or a body height and/or a position of the vehicleoccupant in the vehicle seat can be determined. Further, also theposition of the lower extremities in the area of the footwell can bedetermined, for example.

Detecting and determining the position of the vehicle seat and/or theparameters relating to vehicle occupants can be continuously carried outby the control unit. As an alternative, the position of the vehicle seatand/or the parameters relating to vehicle occupants can be detected anddetermined at fixed intervals. Furthermore, the position of the vehicleseat and/or the parameters relating to vehicle occupants can be detectedand determined as late as when a situation of restraint is given orimmediately before a situation of restraint will occur.

The control unit can determine the presence of a particular situationthrough said sensor data concerning the position of the vehicle seatand/or the parameters relating to vehicle occupants detected by thesensor elements.

The control unit can differentiate between at least two situations.Preferably, the control unit can differentiate between at least fourdifferent situations.

Especially, when the given situation is determined, it can be decisivewhether the vehicle seat is in a standard position or in a comfortposition. It can further be decisive whether the vehicle seataccommodates a person whose body height and/or body weight is within therange of a 5%-person, or a person whose body height and/or body weightis within the range or above the range of a 50%-person. The referencevalues for the 5%-person and the 50%-person in this case are rated to bethe weight and the height of 5%- and 50%-dummies of the hybrid-IIIfamily used in crash tests. The 50%-dummy (“HIII 50% Middle Adult Male”)has a body height of 175 cm and a weight of 78 kg, and the 5%-dummy(“HIII 5% Small Adult Female”) has a body height of 152 cm and a weightof 54 kg.

The value defining the transition between the 5%-person and the50%-person is preferably fixed on the basis of the reference values ofthe 5%-person or the 50%-person. For example, it can be preset to thecontrol unit that a 5%-person is to be assumed up to a body heightand/or a body weight that is 10% above the reference value of the5%-person. Alternatively, it can be preset to the control unit, forexample, that a 50%-person is to be assumed from a body height and/or abody weight that is 10% below the reference value of the 50%-person, andthat a 5%-person is to be assumed in the case of body heights and/orbody weights which are lower than that. These deviation values definingthe exact transition range can be adapted to the respective vehicleoccupant restraint system by those skilled in the art for each specificvehicle.

In one embodiment, the control unit of the vehicle occupant restraintsystem can differentiate, e.g., between the following four possiblesituations:

First situation: the position of the vehicle seat is in a standardposition, and a person whose body height and/or body weight is/arewithin the range of or above a 50%-person is seated in the vehicle seat.

Second situation: the position of the vehicle seat is in a standardposition, and a person whose body height and/or body weight is/are inthe range of a 5%-person is seated in the vehicle seat.

Third situation: the position of the vehicle seat is in a comfortposition, and a person whose body height and/or body weight is/are inthe range of or above a 50%-person is seated in the vehicle seat.

Fourth situation: the position of the vehicle seat is in a comfortposition in which the vehicle seat is shifted backwards vis-à-vis thestandard position, and a person whose body height and/or body weightis/are in the range of a 5%-person is seated in the vehicle seat.

In such embodiment, the control unit can activate the restraint elementsof the vehicle occupant restraint system as explained in the following,for example. The example is shown by way of a vehicle occupant restraintsystem which, as a first restraint element, comprises a knee airbagmodule including a knee airbag with an active depth-adaptive chamberand, as a second restraint element, comprises a foot airbag module and aheel abutting point positioning module.

In the first situation, only the knee airbag module of the firstrestraint element is activated by the control unit.

When the second situation is given, the control unit activates the kneeairbag module and additionally the heel abutting point positioningmodule.

When the third situation is given, the control unit activates the kneeairbag module. Furthermore, the control unit releases a tether, forexample, in the knee airbag module so that the depth-adaptive chambercan be completely filled. In addition, the control unit activates theheel abutting point positioning module.

In the fourth situation, only the foot airbag module is activated. Inthis situation, the shins and the feet of the vehicle occupant swingupwards and impact on the foot airbag of the foot airbag module,especially on a low-pressure chamber of the foot airbag. Thelow-pressure chamber enables the lower extremities of the vehicleoccupant to be absorbed without being rebounded.

In an alternative embodiment of the vehicle occupant restraint systemaccording to the invention, in addition to the foot airbag module theknee airbag module can be activated by the control unit, when the fourthsituation is given.

In another embodiment, the knee airbag may include a pressure-adaptivechamber in the form of a low-pressure chamber. In such embodiment, itmay be provided, for example, that, when the fourth situation is given,only the knee airbag module is activated by the control unit.Alternatively, in such embodiment, when the fourth situation is given,both the knee airbag module and the foot airbag module can be activatedin the situation of restraint.

The afore-described method steps are embodiments which are not limiting.Those skilled in the art may adapt the method according to theinvention, in line with the teaching of the present invention for aspecific vehicle and depending on the existing sensor elements and theseat adjusting options, to further embodiments of the vehicle occupantrestraint system according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention will beevident from the following description of an example embodiment that isunderstood to be not limiting as well as by way of the drawings,wherein:

FIG. 1 shows a schematic view of the footwell of a vehicle with anembodiment of a vehicle occupant restraint system according to theinvention and lower extremities of a 50%-person in a standard position;

FIG. 2 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 1 in an activated state;

FIG. 3 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 1 with lower extremities of a5%-person in a standard position;

FIG. 4 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 3 in an activated state;

FIG. 5 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 1 with lower extremities of a50%-person in a comfort position;

FIG. 6 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 5 in an activated state at a time t1at which feet of the 50%-person impact on a heel abutting pointpositioning module;

FIG. 7 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 5 in an activated state at a time t2at which knees of the 50%-person impact on a knee airbag;

FIG. 8 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 5 in an activated state at a time t2at which knees of the 50%-person impact on an alternative embodiment ofthe knee airbag;

FIG. 9 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 1 with lower extremities of a5%-person in a comfort position;

FIG. 10 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 9 in an activated state at a time t1at which feet of the 5%-person impact on a low-pressure chamber of theknee airbag;

FIG. 11 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 9 in an activated state at a time t2,after feet of the 5%-person have impacted on the low-pressure chamber ofthe knee airbag;

FIG. 12 shows a schematic view of an alternative embodiment of a heelabutting point positioning module in a) a non-activated state and b) anactivated state;

FIG. 13 shows a schematic view of another alternative embodiment of aheel abutting point positioning module in a) a non-activated state andb) an activated state;

FIG. 14 shows a schematic view of the footwell of a vehicle with asecond embodiment of a vehicle occupant restraint system according tothe invention and lower extremities of a 5%-person in a comfort positionin an activated state of the vehicle occupant restraint system at a timet1 immediately before feet of the 5%-person will impact on a footairbag;

FIG. 15 shows a schematic view of the footwell with the vehicle occupantrestraint system according to FIG. 14 at a time t2 after the feet of the5%-person have impacted on the foot airbag;

FIG. 16 shows a schematic view of the footwell with the vehicle occupantrestraint system according to the invention of FIG. 14 with analternative activation of the restraint elements by the control unit ata time t1 immediately before feet of the 5%-person will impact on a footairbag; and

FIG. 17 shows a schematic view of the footwell with the vehicle occupantrestraint system of FIG. 16 at a time t2 after the feet of the 5%-personhave impacted on the foot airbag.

DESCRIPTION

FIG. 1 schematically illustrates a footwell 4 of a vehicle including avehicle occupant protection restraint system 2. The vehicle occupantrestraint system 2 is shown in FIG. 1 in a non-activated state. Thevehicle occupant protection restraint system 2 is configured forprotecting the lower extremities 6 of a vehicle occupant. The lowerextremities comprise, inter alia, the thigh 62, the knee 70, the lowerleg with the shin (tibia) 64 as well as the foot 66 with the heel 68.The lower extremities 6 correspond, as to their dimensions, to the lowerextremities 6 of a 50%-person. The lower extremities 6 are shown in aposition in which the vehicle seat 5 is in a standard position. In FIG.1, merely part of the seating area of the vehicle seat 5 is shown. Thefurther Figures do without a representation of the vehicle seat 5 forreasons of clarity.

The vehicle occupant protection restraint system 2 has a first restraintelement 8 that is in the form of a knee airbag module 12. The kneeairbag module is arranged in a lower area of the instrument panel 3 inthe vehicle vertical direction y. The vehicle occupant protectionrestraint system 2 further comprises a second restraint element 10. Thesecond restraint element 10 is configured as a heel abutting pointpositioning module 14. The heel abutting point positioning module 14 isdisposed in a transition area 39 between a vehicle floor 40 and a frontwall 38 delimiting the footwell 4. The heel abutting point positioningmodule 14 is disposed beneath a vehicle floor lining 42. The vehiclefloor lining 42 may be, for example, a vehicle carpet mounted in thefootwell 4.

FIG. 2 illustrates the vehicle occupant restraint system 2 in anactivated state in a situation of restraint in which a 50%-person isseated in the vehicle seat in a standard position. In the shownembodiment, only the knee airbag module 12 of the first restraintelement 8 is activated by the control unit 100 of the vehicle occupantrestraint system 2. The knee airbag 20 of the knee airbag module 12 inthe shown embodiment comprises plural chambers 22, 24, 26 which areseparated, for example, by tethers 28 and 30. After activation of theknee airbag module 12, the knee airbag 20 is filled with gas by a gasgenerator 11. The lowest chamber 22 in the vehicle longitudinaldirection x of the knee airbag 20 is configured as a pressure-adaptivelow-pressure chamber 22. The low-pressure chamber 22 has a lowerinternal pressure than the two chambers 24 and 26 at the illustratedpoint in time at which the knee 70 and the shin 64 impact on the kneeairbag 20. A forward movement 72 of the lower extremities 6 is limited,on the one hand, by the heel abutting point 18. The heel abutting point18 is arranged in the transition area 39 between the vehicle floor 40and the front wall 38 delimiting the footwell 4 and limits the forwardmovement of the foot 66. On the other hand, the forward movement 72 ofthe lower extremities 6 is limited by the knee airbag 20.

FIG. 3 illustrates the footwell 4 with the lower extremities 7 of a5%-person who is seated in a vehicle seat in the standard position.Further, in dotted lines the lower extremities 6 of a 50%-person areshown. It is evident from the comparison of the lower extremities 7 ofthe 5%-person and the lower extremities 6 that especially the foot 66 ofa 5%-person is further behind in the travel direction x. Consequently, aspace between the heel 68 of the 5%-person and the heel abutting point18 is significantly increased as compared to the space with the50%-person.

As is shown in FIG. 4, in a situation of restraint, apart from the kneeairbag module 12 of the first restraint element 8, also the heelabutting point positioning module 14 is activated. In the shownembodiment, the heel abutting point positioning module 14 comprises anairbag module 34 including a gas generator 33 and an airbag 36. Byfilling the airbag 36 the vehicle floor lining 42 is shifted to theposition marked with 42′. In addition, the heel abutting point 18 isthus shifted backwards in the vehicle longitudinal direction x towardthe foot 66 of the 5%-person to the position marked with 18′.

The vehicle occupant restraint system may include a control unit 100 forcontrolling and activating the first and/or second restraint element(s).The control unit 100 of the vehicle occupant restraint system may beintegrated in a vehicle control system, especially in an airbag controlsystem. In particular, the control unit 100 may be integrated in avehicle control system by which further restraint systems can beadditionally activated and controlled.

For determining the parameters relating to vehicle occupants and/or therelative position of the vehicle seat, the vehicle occupant restraintsystem can comprise at least one sensor element 102. Alternatively, oradditionally, the control unit 100 can access the sensor data of one ormore sensor elements 102 integrated in the vehicle. The sensor element102 may comprise a camera system, for example. Furthermore, the sensorelement 102 can include, e.g., one or more sensors integrated in vehicleseat elements. In addition, the control unit 100 can preferably makealso use of and/or access sensor data of further sensor elementsarranged in the vehicle, especially in the footwell, for detecting thegiven situation.

By displacing the heel abutting point 18 to the position marked with18′, the forward movement of the foot 66 is limited at an early stage inthe situation of restraint, which allows to optimize especially theimmersion of the knee 70 and the shin 64 into the knee airbag of the5%-person. In addition, the shift of the heel abutting point 18 to theposition marked with 18′ prevents the foot 66 and the shin 64 fromswinging upwards.

In FIG. 5, the lower extremities 6′ of a 50%-person are shown who isseated in a vehicle seat 5′ in a comfort position in which the vehicleseat 5′ is shifted backwards compared to the standard position (vehicleseat 5—shown by a dotted line). As compared to the arrangement of thelower extremities 6 in the standard position (shown by a dotted line),the lower extremities 6′ are arranged further behind in the comfortposition.

FIG. 6 illustrates a situation of restraint for the lower extremities 6′of the 50%-person in the comfort position. FIG. 6 shows that, apart fromthe knee airbag module 12 of the first restraint element 8, also theairbag module 34 of the heel abutting point positioning module 14 of thesecond restraint element 10 was activated by the control unit 100. FIG.6 illustrates the vehicle occupant restraint system 2 at a time t1 whenthe foot 66 impacts with the heel 68 on the heel abutting point 18′shifted backwards. Thus, the forward movement of the foot 66 is limitedand, for example, the foot 66 and the shin 64 are prevented fromswinging upwards.

FIG. 7 illustrates the situation of restraint at a subsequent time t2when the knee 70 and the shin 64 impact on the filled knee airbag 20.The protective effect of the knee airbag 12 for the lower extremitiescan be improved by limiting the forward movement of the foot 66 by theheel abutting point positioning module 14.

FIG. 8 illustrates the vehicle occupant restraint system 2 equally atthe time t2. The vehicle occupant restraint system 2 of FIG. 8 differsfrom the vehicle occupant restraint system 2 of FIG. 7 merely by theembodiment of the knee airbag module 12. In the knee airbag module 12 ofFIG. 8, the knee airbag 20′ includes a depth-adaptive chamber 32. Thedepth-adaptive chamber 32 is formed, in the shown example embodiment, bythe tether 30′ being released on one side in the area of the knee airbagmodule 12 by a release unit. In this way, in the area of the two upperchambers 24 and 26 the knee airbag 20′ can expand further toward thelower extremities 6′ of the vehicle occupant. The release unit forreleasing the tether 30′ is activated by the control unit 100.

In FIG. 9, the lower extremities 7′ of a 5%-person seated in a vehicleseat 5′ in a comfort position are shown. In comparison with thearrangement of the lower extremities 6 of the 50%-person (shown by adotted line) and lower extremities 7 of the 5%-person (shown by adash-dot line) in the vehicle seat 5 in the standard position (shown bya dotted line), the lower extremities 7′ are arranged still furtherbehind in the comfort position.

In FIG. 10 a situation of restraint for the lower extremities 7′ of the5%-person in the comfort position is illustrated. FIG. 10 shows thevehicle occupant restraint system 2 at a time t1 when the foot 66impacts on the lowest chamber 22 of the knee airbag 20. The chamber 22is configured as a low-pressure chamber 22 which, in a filled state orat least when the feet 66 impact on the knee airbag 20, has a lowerinternal pressure than the two further chambers 24 and 26 of the kneeairbag.

In the illustrated embodiment, only the knee airbag module 12 of thefirst restraint element 8 is activated by the control unit 100. The heelabutting point positioning module 14 is not activated in the shownvehicle occupant restraint system 2. In the illustrated embodiment, theactivation does not take place especially because it was determined bythe control unit 100 that the heel abutting point 18′ shifted backwardscould not prevent the foot 66 and the shin 64 from swinging upwards.

FIG. 11 shows the restraint situation of FIG. 10 at a later point intime t2 when the feet 66 of the vehicle occupant have already impactedon the low-pressure chamber 22. The lower internal pressure of thelow-pressure chamber 22 enable the feet 66 to “immerse” into thelow-pressure chamber 22. Thus, rebounding of the feet 66 and the shins64 can be prevented or at least weakened.

FIGS. 12 and 13 illustrate alternative embodiments of the heel abuttingpoint positioning module 14′ and 14″. For the heel abutting pointpositioning modules 14′ and 14″ the shift of the heel abutting point 18to the position marked with 18′ is carried out via a deformationelement.

In the heel abutting point positioning module 14′ shown in FIG. 12 a)and b), the deformation element is configured as a bistable springelement 44. The bistable spring element is disposed beneath the vehiclefloor lining 42 in the transition area 39 between the front wall 38delimiting the footwell 4 and the vehicle floor 40.

The bistable spring element 44 can be excited by an actuator 48 tochange its shape from the first stable position shown in FIG. 12 a) to asecond stable position shown in FIG. 12 b).

In the heel abutting point positioning module 14″ shown in FIG. 13 a)and b), the deformation element is represented as a foamable element 46.The foamable element 46 comprises a material 47 which can be foamed byexcitation and thus increases its volume. The foamable element 46 isdisposed beneath the vehicle floor lining 42 in the transition area 39between the front wall 38 delimiting the footwell 4 and the vehiclefloor 40.

Upon activation of the heel abutting point positioning module 14″, thefoaming process is started by the control unit 100 by an appropriateactuator 48′. The vehicle floor lining 42 is lifted by the foamedmaterial 47′ into the position marked with 42′. The heel abutting point18 is shifted by the foamed material toward the vehicle occupant to theposition marked with 18′. The vehicle floor lining 42 can be fixed atthe shifted heel abutting point 18′ on the vehicle floor 40 so as toobtain a defined shift of the heel abutting point 18 to the positionmarked with 18′.

FIGS. 14 and 15 illustrate another embodiment of the vehicle occupantrestraint system 2 with the lower extremities 7′ of a 5%-person in avehicle seat 5′ in a comfort position in which the vehicle seat 5′ isshifted backwards. For the purpose of comparison, in FIG. 14 the vehicleseat 5 is additionally shown in dotted line in the standard position.The vehicle occupant restraint system 2 differs from the vehicleoccupant protection system 2 of FIGS. 1 to 11 in that the knee airbag 21of the knee airbag module 12 includes no low-pressure chamber. Moreover,the second restraint element 10 comprises a foot airbag module 16 inaddition to the heel abutting point positioning module 14.

In the shown example embodiment, the control unit 100 has activated theknee airbag module 12 of the first restraint element 8 as well as thefoot airbag module 16 of the second restraint element 10 for the givensituation. FIG. 14 illustrates the situation of restraint at a time t1immediately before the foot 66 impacts on a foot airbag 50. Further,FIG. 15 illustrates the situation of restraint at a time t2 after thefoot 66 has impacted on and “immersed” into the foot airbag 50. In thefurther points, the shown situation of restraint corresponds to thesituation of restraint shown in FIGS. 10 and 11.

The foot airbag 50 of the foot airbag module 16 is configured as alow-pressure chamber 52. The low-pressure chamber 52 in the filled statehas a lower internal pressure than the chambers 25 and 27 of the kneeairbag 21 of the knee airbag module 12 of the first restraint element 8.

In the installed state, the foot airbag module 16 is disposed in thelower area of the instrument panel 3 ahead of the knee airbag module 12(relating to the vehicle vertical direction y and the vehiclelongitudinal direction x).

In the shown example embodiment of FIGS. 14 and 15, the low-pressurechamber 52 of the foot airbag 50 substantially adopts the function ofthe pressure-adaptive low-pressure chamber 22 of the knee airbag 20 ofthe example embodiment shown in FIGS. 1 to 11.

In particular, also the low-pressure chamber 52 enables the feet 66, dueto the lower internal pressure, to “immerse” into the low-pressurechamber 52. Thus, in this case rebounding of the feet 66 and of theshins 64 can equally be prevented or at least weakened.

The foot airbag module 16 in such embodiment of the vehicle occupantrestraint system 2 is only activated, for example, if a 5%-person isseated in the vehicle seat in the comfort position.

FIGS. 16 and 17 illustrate a vehicle occupant restraint system 2 withthe lower extremities 7′ of a 5%-person in a vehicle seat 5′ in acomfort position which, as to its structure, corresponds to the vehicleoccupant restraint system 2 of the FIGS. 14 and 15. In the comfortposition, the vehicle seat 5′ is shifted backwards as compared to thevehicle seat 5 in the standard position (shown in dotted line).

The vehicle occupant restraint system 2 of FIGS. 16 and 17 differs fromthe vehicle occupant restraint system 2 of FIGS. 14 and 15 by analternative activation of the restraint elements in a situation ofrestraint, when a particular situation is given.

The particular situation is given if it is detected by the control unit100 that the vehicle seat 5 is in a position shifted backwards,especially in a comfort position, and the vehicle occupant is a shortand/or light person, especially a 5%-person.

When said particular situation is given, only the foot airbag module 16of the second restraint element 10 is activated by the control unit 100.In the further possible situations in which the vehicle seat is in astandard position and/or in the vehicle seat a person is seated who istaller and/or heavier than a 5%-person, at least the knee airbag module12 of the first restraint element 8 is activated by the control unit100. Depending on the situation, moreover the foot airbag module 16and/or the heel abutting point positioning module 14 of the secondrestraint element 10 can be activated by the control unit 100.

What is claimed is:
 1. A vehicle occupant restraint system comprising acontrol unit and at least two restraint elements for the protection oflower extremities in the area of a footwell of a vehicle of a vehicleoccupant seated in a particular vehicle seat of the vehicle, wherein afirst restraint element is in the form of a knee airbag module, whereina second restraint element is provided for mounting into the footwell ofthe vehicle in an area of the footwell of the vehicle arranged in thevehicle longitudinal direction ahead of the knee airbag module, whereinthe second restraint element comprises at least one foot airbag moduleincluding a foot airbag, wherein the control unit can differentiate, ina situation of restraint, between different given situations, the givensituation being determinable via a vehicle seat position and parametersrelating to vehicle occupants, wherein the control unit in the situationof restraint, when a situation is given in which the vehicle occupant isa short and/or light person and the vehicle seat is in a positionshifted backwards, in a position shifted backwards compared to astandard position, only activates the foot airbag module of the secondrestraint element.
 2. The vehicle occupant restraint system according toclaim 1, wherein, in a situation in which the vehicle seat is in thestandard position and/or the vehicle occupant is not a short and/orlight person, in the situation of restraint at least the knee airbagmodule of the first restraint element is activated by the control unit,wherein the control unit can additionally activate, depending on thegiven situation, the second restraint element or a partial element ofthe second restraint element.
 3. The vehicle occupant restraint systemaccording to claim 1, wherein the second restraint element comprises aheel abutting point positioning module.
 4. The vehicle occupantrestraint system according claim 1, wherein the foot airbag of the footairbag module comprises a low-pressure chamber or is configured as alow-pressure chamber.
 5. The vehicle occupant restraint system accordingclaim 1, wherein the knee airbag module comprises a knee airbag with atleast one adaptive chamber.
 6. The vehicle occupant restraint systemaccording to claim 5, wherein the adaptive chamber of the knee airbagcan be activated and/or controlled through the control unit.
 7. Thevehicle occupant restraint system according claim 1, wherein a kneeairbag of the knee airbag module comprises a pressure-adaptive chamber.8. The vehicle occupant restraint system according to claim 7, whereinthe pressure-adaptive chamber of the knee airbag is in the form of alow-pressure chamber.
 9. The vehicle occupant restraint system accordingclaim 1, wherein a knee airbag of the knee airbag module comprises adepth-adaptive chamber.
 10. The vehicle occupant restraint systemaccording claim 3, wherein the heel abutting point positioning modulecomprises an airbag module.
 11. The vehicle occupant restraint systemaccording claim 3, wherein the heel abutting point positioning modulecomprises a deformation element.
 12. The vehicle occupant restraintsystem according to claim 11, wherein the deformation element comprisesa bistable spring element.
 13. The vehicle occupant restraint systemaccording to claim 11, wherein the deformation element comprises afoamable element.
 14. The vehicle occupant restraint system accordingclaim 1, comprising at least one sensor element for detecting the givensituation.
 15. The vehicle occupant restraint system according to claim14, wherein the sensor element comprises a camera system and/or sensorsdisposed and/or integrated in vehicle seat elements and/or in thefootwell.
 16. A method for operating a vehicle occupant restraint systemaccording claim 1, said method comprising the following steps of:detecting and determining a position of the vehicle seat and/orparameters relating to vehicle occupants in a situation of restraint;determining the given situation by the control unit; activating therestraint elements and/or partial elements of the restraint elementsrequired for the restraint in the given situation.
 17. The method foroperating a vehicle occupant restraint system according to claim 16,wherein, when detecting the parameters relating to vehicle occupants, abody weight and/or a body height and/or a position of the vehicleoccupant in the vehicle seat is/are determined.